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Connecting Your Computer to a Sound System
Connecting a computer to a sound system is fairly simple and easy but sometimes can be made hard by facility people whose only knowledge of playing music is to put a microphone up to a speaker (this is bad for the mic, the speaker and the sound system, do not attempt).

Below, is a step-by-step, item-by-item description on what you need and how you need to connect your computer to a sound system with differing inputs.

First you will need the proper items to hook up to your sound system.  


Ground Loop Isolator from Radio Shack
This prevents the hum you sometimes hear coming from your sound system.  The computer you use puts more power out than a normal piece of audio equipment like a CD, tape or mini-disc player.  The Ground Loop Isolator (or "GLI" as some sound companies call it) cuts down on this power and eliminates the hum.  I installed several of these into new computerized sound systems in Northern Virginia and noticed a great difference.  The "GLI" comes with a Y-adaptor that goes from 2-RCA to an 1/8-inch stereo plug that goes right into your computer.  Approximate cost is about $10, but well worth the investment.  The "GLI" is about 6 feet in length and a picture of the one I use is shown below.  On some mixers (mostly from Radio Shack) this is all that you would need to hook into the sound system.

2 RCA to 1/4" male Y-Adaptor
You will need this to connect the "GLI" to mixers with 1/4" female inputs.  Most of the mid-range and higher quality mixers will need this.  A lot of people will just find one at Radio Shack and buy it but you have to look at the bigger end.  DO NOT get a stereo end because it will divide the sound.  Play a song like "Good Lovin" or even "Rock and Roll Pt. 2 (The Hey Song)" on your car stereo.  Take the balance and put it all the way to one side.  You don't get the whole song and it sounds really funky.  You always want to use mono plugs when connecting to sound systems (there are some cases where you'd use stereo, but that's more for DJ work than game production).
  All audio mixer inputs are in mono and do not use stereo.  Using a 1/4" stereo is not recommended.  If you find you have made this mistake, you are not alone.  This item will generally cost you $2-5 depending on the kind you get.  There is a silver adaptor that looks like a "Y", there are others that are about 3-5 inches in length.  I always prefer to use gold connectors and have found this model above and the silver Y-adaptor to be the most rugged and less likely to malfunction.


Extra accessories you may need to add
The two accessories you see above are also found at Radio Shack and may be needed depending on the kind of inputs you have.  I have found that a lot of schools who pick up the industrial mixers or only have an XLR input to plug your entire sound system into will need one, if not both.
1/4" Female to Male XLR
XLR is the "three-pronged" end you see on most microphones.  This adaptor is also known as "The Post" because of it's length of 4 1/2 inches, plus it sticks up like a post.  Use this when your XLR input is a female.  The Post will run you about $12 from Radio Shack.
Female XLR to Female XLR
Simple adaptor for when the XLR input is a male instead of female.  This is a funny item to price because I got the one you see in the photo for $8 while I have seen them from $5 to $15.  Radio Shack is still the best for this.

Connecting to your sound system now that you have all the parts

1.  Connect the "GLI" to your computer, make sure the computer is off.  Do this the first time.  Each time after, connect the lines to the sound system/mixer before plugging the "GLI" into the computer.  The proper way to connect the "GLI" to the computer is to attach the Y-adaptor that came with the "GLI" (match the colors) to the shorter end as noted by the picture below.  This may be the last step you need if you are using a Radio Shack mixer or amplifier that uses RCA inputs.

2.  Connect the RCA-1/4" Y-adaptor to the other end of the "GLI" line.  This may be the last step you need (it is on the set-up I use for the Modesto A's).
3.  Connect "The Post" (1/4 female to male XLR) to the RCA-1/4" Y-adaptor.  This was the last step I used when connecting to quite a few high school sound systems.  A lot of city building will use this set-up.  I've seen this in schools, government centers, office building, college arenas, etc.  You will want to have a Post with you if you move around and use different systems. 

4.  In the event the XLR input is a male (like it is at W. T. Woodson High School and several other Fairfax County High Schools), you'll need to then connect the "female XLR to female XLR" to the Post so you can connect to the system.
If you are connecting your computer to your mixer and then to the sound system, you'll need a connection from the output of the mixer to the sound system.  Steps 2-4 also serve as a instructions on how to connect to a sound system.  Instead of the "GLI", you'll use a 2-RCA to 2-RCA.  Most outputs from mixers are RCA.  On my Modesto A's set-up, I have two 1/4" outputs so I picked up a pair of 1/4" male to RCA female then connected to a 2-RCA to 2-RCA monster cable (50 feet in length because of the distance between the mixer and the rack).  Make sure when purchasing your items that you give yourself enough length.  Six feet usually is the best.  I will rarely use three-foot lengths and I do mean rarely.  Even the Modesto A's set-up which is in it's own case has six-foot lines running through it.  If you have any questions or comments on the set-up, please feel free to e-mail me.